Lumbar disc herniation [1] [2] [3] (Figure 1(a)) is a medical condition affecting the spine in which a tear in the outer, fibrous ring of an intervertebral disc allows the soft, central portion to bulge out beyond the damage outer rings (Figure 1(b)). Also known as slipped disc, it is commonly related to age degeneration of the outer ring, known as the annulus fibrous [4] [5] . A Lumbar disc herniation may develop suddenly or gradually over weeks or months. The 4 stages to a herniated disc are: Disc degeneration, Prolapse, extrusion and sequestration or sequestered disc [6] [7] [8] (Figure 1(c)). Lumbar disc herniation may be located as central prolapse, Posterolateral (paracentral), foraminal and axial. Lumbar disc herniation may cause severe pain even in the absence of nerve root compression. The common regions for Lumbar disc herniation are between 4th and 5th lumbar vertebral bodies and between 5th lumbar vertebrae and Sacrum [4] [7] . Symptoms of herniated disc range from little or no pain to severe lower back pain that will radiate into the portion served by affected nerve roots that are irritated or impinged by the herniated materials. Numbness, tingling, parasthesia and motor changes like muscle weakness, paralysis and affection of reflexes are the symptoms [9] [10] . In LDH, the patient may also experience sciatica due to irritation of sciatic nerve [11] . Radiating pain may result from prolapsed disc in the lumbar spine. In case that the prolapsed is large and presses on nerves within the spinal column or the cauda equine, both sides of the body may be affected, often with serious consequences [6] [12] . Diagnosis of herniation is based on the history, symptoms and physical examination [13] . Investigations are performed to confirm and rule out other causes as spondylolisthesis, tumors, and metastasis as well as for treatment option of herniation. X-ray, CT and MRI (Figure 1(d)) are the choice of investigations [9] [13] .

Lumbar spine stenosis [17] [18] [19] is a medical condition described by Verbiest [20] in 1950 in which the spinal canal narrows and compresses the nerves at the level of the lumbar vertebrae (Figure 2). Spinal degeneration that occurs with aging is the common cause of LSS [18] . It can also be due to osteoporosis, spinal disc herniation or tumors. It can be also due to congenital conditions [21] . LSS may cause low back pain, abnormal sensations and the absence of sensations (numbness) in the legs, thighs, feet or buttocks, or loss of bladder and bowel control [21] . Symptoms include pain or cramping in the legs when standing for long periods or when walking [9] [21] . The discomfort usually eases when bending forward or sitting down. The first symptoms of LSS include low back pain. After few months and years, that may progress to claudication [21] [22] . The LSS is most common in older community and retirement communities [23] .

The diagnosis of LSS is based on clinical findings. When a patient presents with the typical symptoms of lumbar spinal stenosis (leg pain, with or without back pain, which is aggravated by walking), a conclusive diagnosis is made using imaging studies from an MRI scan or a CT scan with myelogram (using an x-ray dye in the spinal sack fluid) [25] [26] . Physical examination alone does not yield a conclusive LSS diagnosis. LSS can be central, lateral or foraminal stenosis (Figure 3) [27] . Plain X-rays may or may not show LSS. CT and MRI scanning are done for the definitive diagnosis of LSS.

The concept of minimally invasive surgery for lumbar region is to provide surgical options without producing iatrogenic morbidity associated with the open surgical procedures. In 1973 Kambin and Gellmann in United States [29] , and in 1975 Hijikata in Japan [30] , independently performed a non-visualized percutaneous technique via a posteriolateral approach. In 1983, the direct visualization of the intervertebral disc space with modified arthroscope was report by Forst and Housaman [31] . In 1988, Kambin was the first to publish intraoperative discoscopic view of a herniated nucleus pulposus [32] . A “Percutaneous discoscopy” a bipolar endoscopic posterolateral techniques with modified instruments for direct view was described by Schreiber in 1989 and 1991 [33] [34] . In 1992 Mayer introduced percutaneous endoscopic laser discectomy combining forceps and laser [35] . Mayer and Brock described the technique for disc herniation by using angled optics for viewing the dorsal aspect of annular tear. The concept of posterolateral endoscopic lumbar nerve decompression changed from indirect central nucleotomy (inside out, in which fragments are extracted through an annular fenestration outside the spinal canal) to transforaminal direct extraction of the non-contained and sequestered disc fragments from inside the spinal canal. With the effort of Yeung et al., the present single portal endoscopic discectomy is possible. Originally, this technique was devised for the treatment of lumbar disc herniation only. Yeaung and Knight used a holmium-YAG (yttrium-almunium-garnet)-laser for ablation of bony and soft tissue for decompression, enhanced access and to improve intracanal visualization [36] [37] . In 1997 Yeung developed Yeung Endoscopic Spine System (YESS) and in 1994 Hoogland developed the Thomas Hoogland Endoscopic Spine System (THESSYS) [38] . With THESSYS, enlargement of the intervertebral foramen near the facet joint with special reamers is possible which help to reach intracanal extruded and sequestered disc fragments and decompress foraminal stenosis [39] . With the advances in technology and increasing experiences, percutaneous lumbar surgery is gradually expanding day by day. Modern endoscopic surgeons are able to deal with treatment of lumbar stenosis with this procedure. Percutaneous endoscopic surgery has been regarded as a safe, minimally invasive procedure. Since 2000, various advanced endoscopic techniques have been developed to perform decompression under direct view and local anesthesia. The concept of endoscopic lumbar surgery is the reduction of lumbar segmental pain by removal of casual pain sources. The procedure involves enlargement of the foramen by removal of disc compression, removal of osteophytes impacting upon the nerve, removal of ligaments impinging upon the nerve, shrinkage of redundant annulus and removal of perineural scarring or granulation tissue.

The surgical instruments of percutaneous endoscopic surgery consist (Figure 4):

a) Working channel endoscope with angle optics.

b) Flexible forceps, which can reach the intended site and dissect or decompress any lesions around the endoscopic field.

c) Steerable radiofrequency coagulator for coagulation or ablation of soft tissues.

d) Articulating bone burr, which can remove wide range of bone tissues.

e) Endoscopic punch that can remove bone and soft tissues under endoscopic vision.

The pathological zone determines the Choice of approach. The patient is placed in prone position on a radiological compatible table (Figure 5). Cannula

insertion point is confirmed before surgery by the guidance of CT and MRI. The procedure is performed under local anesthesia with regular monitoring of the vitals of the patient. 1% lidocaine is the choice for local anesthesia given at the distance of 8 to 12 cm from the midline of the back (Figure 6). Under the local anesthesia the surgeon uses a 25 cm 18 gauge needle to place it in the disc space through Kambin’s triangle (Figure 7) [40] [41] , which is the safe region. Further, discography is conducted to dye the nucleus polposus. The procedure is done under proper visualization taken by C-arm in both anteroposterior and lateral view.

A guide wire was inserted in the disc through the needle channel. The needle is removed and a bluntly tapered tissue dilating obturator was slipped over the guide wire till its tip firmly engaged in the annular window (Figure 8(a) & Figure 8(b)), then an endoscope was inserted into the working sleeve. Later, the

working zone and the annulus fibrous were observed and working sleeve is pushed into the disc space. Decompression is continued under a direct clear visual field and constant saline irrigation. After complete decompression, the dural sac and lumbar exiting nerve root is checked for free movable (Figure 8(c)). Bleeding of small vessels is controlled by bipolar frequency probe. After the decompression, all the instruments are removed carefully. A single or two skin stiches are given at the incision point. Communication is maintained with patient throughout the surgical procedure.

ODI is an index derived from the Oswestry Low Back Pain Questionnaire used by clinicians and researchers to quantify disability for low back pain. The Oswestry Disability Index is currently considered by many as the gold standard for measuring degree of disability and estimating quality of life in a person with low back pain. The self-completed questionnaire contains ten topics concerning intensity of pain, lifting, ability to care for oneself, ability to walk, ability to sit, sexual function, ability to stand, social life, sleep quality, and ability to travel. 6 statements describing different potential scenarios in the patient’s life relating to the topic follow each topic category. The patient then checks the statement, which most closely resembles their situation. Each question is scored on a scale of 0 - 5 with the first statement being zero and indicating the least amount of disability and the last statement is scored 5 indicating most severe disability. The scores for all questions answered are summed, and then multiplied by two to obtain the index (range 0 to 100) (Table 1). Zero is equated with no disability and 100 are the maximum disability possible.

VAS is a measurement instrument that tries to measure a characteristic or attitude that is believed to range across a continuum of values and cannot easily be directly measured. For example, the amount of pain that a patient feels ranges across a continuum from none to an extreme amount of pain. From the patient's perspective this spectrum appears continuous ± their pain does not take discrete jumps, as a categorization of none, mild, moderate and severe would suggest. To capture this idea of an underlying continuum, the VAS was devised.

Macnab’s outcome is based on assessment of patient satisfaction. The patient is asked to rate his level of well-being, generally after surgery. The patient choose

one of the four: Excellent, Good, Fair, Poor (Excellent: no pain, no restriction of mobility, return to normal work and level of activity; Good: occasional non radicular pain, relief of presenting symptoms, able to return to modified work; Fair: some improved functional capacity, still handicapped and/or unemployed; Poor: continued objective symptoms of root involvement, additional operative intervention needed at the index level irrespective of the length of postoperative follow-up).

The reviews of different original articles were done which focus on the Percutaneous Endoscopic Lumbar surgery. Different search engine as GOOGLE SCHOLAR, PUBMED, SCOPUS and RESEARCHGATE were used to find out the published articles that were related with the LDH, LSS and Percutaneous Endoscopy Lumbar Surgery (Figure 9).

Around 97 Lumbar spines related articles were studied of which 48 articles were extracted which were either related to LDH, LSS or PTELSS. Of 48 articles only 25 articles were extracted which were related to Endoscopic Lumbar Spine Surgery done for LDH. But we included only those articles which were published after 2009 onwards, so that we can analyze the recent advancement and updates regarding Transforaminal endoscopic Lumbar Spine Surgery. Thus, 11 articles were included which focused on Transforaminal technique but one article deals with less than 30 number of cases due to which we excluded the particular article. Finally, we have 10 articles for the review and all these articles presented with clinical outcomes on the basis of either Macnab criteria, VAS score or ODI score (Table 2). The review mainly emphasizes on the clinical outcome of Percutaneous Transforaminal Endoscopic Lumbar Spine Surgery associated with or without the surgical complications.

Till now there have been a number of articles published regarding the Percutaneous Transforaminal approach for Lumbar disc herniation. But only few of the articles deal with the Transforaminal approach for Lumbar Stenosis. Since, the surgery requires expert endoscopic surgeon, only the well-trained surgeon preferred to do transforaminal approach for lumbar stenosis. Thus, in this section few articles have been mentioned which deals with the transforaminal approach for lumbar stenosis. Three studies [55] [56] [57] described the use of the transforaminal endoscopic technique for disc herniation with central lumbar stenosis. Most cases involved lumbar disc herniation combined with lumbar stenosis, and the results were not reported for the stenosis subgroup. In Kambin P, Casey K, O’Brien E et al. [58] 82% of patients with lateral recess stenosis rated the results as satisfactory that underwent PTED. Bingtao Wen, Xifeng Zhang, Lin Zhang et al. [59] retrospectively studied 64 patients with lumbar stenosis who underwent Percutaneous Endoscopic Lumbar Spine Decompression. The mean preoperative VAS score was 7.7+/−1.2, while Postoperative 3 months, 6 months and final follow-up VAS scores were 2.8+/−0.7, 2.1+/−0.6, and 0.8+/−0.6, respectively (P < 0.001). The mean preoperative ODI score was 72+/−1.2, while postoperative 3 months, 6 months, and final follow-up ODI scores were 29.7+/−4.9, 23.9+/−4.0, and 12.5+/−3.9, respectively (P < 0.0010). The excellent and good rate reached 73.4% at the final follow-up. No complication was seen intraoperative and postoperatively.